
#include "skbitmap_operations.h"

#include <algorithm>
#include <string.h>

#include "base/logging.h"

#include "SkBitmap.h"
#include "SkCanvas.h"
#include "SkColorPriv.h"
#include "SkUnPreMultiply.h"

// static
SkBitmap SkBitmapOperations::CreateInvertedBitmap(const SkBitmap& image)
{
    DCHECK(image.config() == SkBitmap::kARGB_8888_Config);

    SkAutoLockPixels lock_image(image);

    SkBitmap inverted;
    inverted.setConfig(SkBitmap::kARGB_8888_Config,
        image.width(), image.height(), 0);
    inverted.allocPixels();
    inverted.eraseARGB(0, 0, 0, 0);

    for(int y=0; y<image.height(); ++y)
    {
        uint32* image_row = image.getAddr32(0, y);
        uint32* dst_row = inverted.getAddr32(0, y);

        for(int x=0; x<image.width(); ++x)
        {
            uint32 image_pixel = image_row[x];
            dst_row[x] = (image_pixel&0xFF000000) |
                (0x00FFFFFF - (image_pixel&0x00FFFFFF));
        }
    }

    return inverted;
}

// static
SkBitmap SkBitmapOperations::CreateSuperimposedBitmap(const SkBitmap& first,
                                                      const SkBitmap& second)
{
    DCHECK(first.width() == second.width());
    DCHECK(first.height() == second.height());
    DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
    DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

    SkAutoLockPixels lock_first(first);
    SkAutoLockPixels lock_second(second);

    SkBitmap superimposed;
    superimposed.setConfig(SkBitmap::kARGB_8888_Config,
        first.width(), first.height());
    superimposed.allocPixels();
    superimposed.eraseARGB(0, 0, 0, 0);

    SkCanvas canvas(superimposed);

    SkRect rect;
    rect.fLeft = 0;
    rect.fTop = 0;
    rect.fRight = SkIntToScalar(first.width());
    rect.fBottom = SkIntToScalar(first.height());

    canvas.drawBitmapRect(first, NULL, rect);
    canvas.drawBitmapRect(second, NULL, rect);

    return superimposed;
}

// static
SkBitmap SkBitmapOperations::CreateBlendedBitmap(const SkBitmap& first,
                                                 const SkBitmap& second,
                                                 double alpha)
{
    DCHECK((alpha>=0) && (alpha<=1));
    DCHECK(first.width() == second.width());
    DCHECK(first.height() == second.height());
    DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
    DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

    // Optimize for case where we won't need to blend anything.
    static const double alpha_min = 1.0 / 255;
    static const double alpha_max = 254.0 / 255;
    if(alpha < alpha_min)
    {
        return first;
    }
    else if(alpha > alpha_max)
    {
        return second;
    }

    SkAutoLockPixels lock_first(first);
    SkAutoLockPixels lock_second(second);

    SkBitmap blended;
    blended.setConfig(SkBitmap::kARGB_8888_Config,
        first.width(), first.height(), 0);
    blended.allocPixels();
    blended.eraseARGB(0, 0, 0, 0);

    double first_alpha = 1 - alpha;

    for(int y=0; y<first.height(); ++y)
    {
        uint32* first_row = first.getAddr32(0, y);
        uint32* second_row = second.getAddr32(0, y);
        uint32* dst_row = blended.getAddr32(0, y);

        for(int x=0; x<first.width(); ++x)
        {
            uint32 first_pixel = first_row[x];
            uint32 second_pixel = second_row[x];

            int a = static_cast<int>((SkColorGetA(first_pixel) * first_alpha) +
                (SkColorGetA(second_pixel) * alpha));
            int r = static_cast<int>((SkColorGetR(first_pixel) * first_alpha) +
                (SkColorGetR(second_pixel) * alpha));
            int g = static_cast<int>((SkColorGetG(first_pixel) * first_alpha) +
                (SkColorGetG(second_pixel) * alpha));
            int b = static_cast<int>((SkColorGetB(first_pixel) * first_alpha) +
                (SkColorGetB(second_pixel) * alpha));

            dst_row[x] = SkColorSetARGB(a, r, g, b);
        }
    }

    return blended;
}

// static
SkBitmap SkBitmapOperations::CreateMaskedBitmap(const SkBitmap& rgb,
                                                const SkBitmap& alpha)
{
    DCHECK(rgb.width() == alpha.width());
    DCHECK(rgb.height() == alpha.height());
    DCHECK(rgb.bytesPerPixel() == alpha.bytesPerPixel());
    DCHECK(rgb.config() == SkBitmap::kARGB_8888_Config);
    DCHECK(alpha.config() == SkBitmap::kARGB_8888_Config);

    SkBitmap masked;
    masked.setConfig(SkBitmap::kARGB_8888_Config, rgb.width(), rgb.height(), 0);
    masked.allocPixels();
    masked.eraseARGB(0, 0, 0, 0);

    SkAutoLockPixels lock_rgb(rgb);
    SkAutoLockPixels lock_alpha(alpha);
    SkAutoLockPixels lock_masked(masked);

    for(int y=0; y<masked.height(); ++y)
    {
        uint32* rgb_row = rgb.getAddr32(0, y);
        uint32* alpha_row = alpha.getAddr32(0, y);
        uint32* dst_row = masked.getAddr32(0, y);

        for(int x=0; x<masked.width(); ++x)
        {
            SkColor rgb_pixel = SkUnPreMultiply::PMColorToColor(rgb_row[x]);
            int alpha = SkAlphaMul(SkColorGetA(rgb_pixel), SkColorGetA(alpha_row[x]));
            dst_row[x] = SkColorSetARGB(alpha,
                SkAlphaMul(SkColorGetR(rgb_pixel), alpha),
                SkAlphaMul(SkColorGetG(rgb_pixel), alpha),
                SkAlphaMul(SkColorGetB(rgb_pixel), alpha));
        }
    }

    return masked;
}

// static
SkBitmap SkBitmapOperations::CreateButtonBackground(SkColor color,
                                                    const SkBitmap& image,
                                                    const SkBitmap& mask)
{
    DCHECK(image.config() == SkBitmap::kARGB_8888_Config);
    DCHECK(mask.config() == SkBitmap::kARGB_8888_Config);

    SkBitmap background;
    background.setConfig(SkBitmap::kARGB_8888_Config,
        mask.width(), mask.height(), 0);
    background.allocPixels();

    double bg_a = SkColorGetA(color);
    double bg_r = SkColorGetR(color);
    double bg_g = SkColorGetG(color);
    double bg_b = SkColorGetB(color);

    SkAutoLockPixels lock_mask(mask);
    SkAutoLockPixels lock_image(image);
    SkAutoLockPixels lock_background(background);

    for(int y=0; y<mask.height(); ++y)
    {
        uint32* dst_row = background.getAddr32(0, y);
        uint32* image_row = image.getAddr32(0, y % image.height());
        uint32* mask_row = mask.getAddr32(0, y);

        for(int x=0; x<mask.width(); ++x)
        {
            uint32 image_pixel = image_row[x % image.width()];

            double img_a = SkColorGetA(image_pixel);
            double img_r = SkColorGetR(image_pixel);
            double img_g = SkColorGetG(image_pixel);
            double img_b = SkColorGetB(image_pixel);

            double img_alpha = static_cast<double>(img_a) / 255.0;
            double img_inv = 1 - img_alpha;

            double mask_a = static_cast<double>(SkColorGetA(mask_row[x])) / 255.0;

            dst_row[x] = SkColorSetARGB(
                static_cast<int>(std::min(255.0, bg_a + img_a) * mask_a),
                static_cast<int>(((bg_r * img_inv) + (img_r * img_alpha)) * mask_a),
                static_cast<int>(((bg_g * img_inv) + (img_g * img_alpha)) * mask_a),
                static_cast<int>(((bg_b * img_inv) + (img_b * img_alpha)) * mask_a));
        }
    }

    return background;
}

namespace
{

    namespace HSLShift
    {

        // TODO(viettrungluu): Some things have yet to be optimized at all.

        // Notes on and conventions used in the following code
        //
        // Conventions:
        //  - R, G, B, A = obvious; as variables: |r|, |g|, |b|, |a| (see also below)
        //  - H, S, L = obvious; as variables: |h|, |s|, |l| (see also below)
        //  - variables derived from S, L shift parameters: |sdec| and |sinc| for S
        //    increase and decrease factors, |ldec| and |linc| for L (see also below)
        //
        // To try to optimize gfx::HSL shifts, we do several things:
        //  - Avoid unpremultiplying (then processing) then premultiplying. This means
        //    that R, G, B values (and also L, but not H and S) should be treated as
        //    having a range of 0..A (where A is alpha).
        //  - Do things in integer/fixed-point. This avoids costly conversions between
        //    floating-point and integer, though I should study the tradeoff more
        //    carefully (presumably, at some point of processing complexity, converting
        //    and processing using simpler floating-point code will begin to win in
        //    performance). Also to be studied is the speed/type of floating point
        //    conversions; see, e.g., <http://www.stereopsis.com/sree/fpu2006.html>.
        //
        // Conventions for fixed-point arithmetic
        //  - Each function has a constant denominator (called |den|, which should be a
        //    power of 2), appropriate for the computations done in that function.
        //  - A value |x| is then typically represented by a numerator, named |x_num|,
        //    so that its actual value is |x_num / den| (casting to floating-point
        //    before division).
        //  - To obtain |x_num| from |x|, simply multiply by |den|, i.e., |x_num = x *
        //    den| (casting appropriately).
        //  - When necessary, a value |x| may also be represented as a numerator over
        //    the denominator squared (set |den2 = den * den|). In such a case, the
        //    corresponding variable is called |x_num2| (so that its actual value is
        //    |x_num^2 / den2|.
        //  - The representation of the product of |x| and |y| is be called |x_y_num| if
        //    |x * y == x_y_num / den|, and |xy_num2| if |x * y == x_y_num2 / den2|. In
        //    the latter case, notice that one can calculate |x_y_num2 = x_num * y_num|.

        // Routine used to process a line; typically specialized for specific kinds of
        // gfx::HSL shifts (to optimize).
        typedef void (*LineProcessor)(gfx::HSL, const SkPMColor*, SkPMColor*, int width);

        enum OperationOnH { kOpHNone = 0, kOpHShift, kNumHOps };
        enum OperationOnS { kOpSNone = 0, kOpSDec, kOpSInc, kNumSOps };
        enum OperationOnL { kOpLNone = 0, kOpLDec, kOpLInc, kNumLOps };

        // Epsilon used to judge when shift values are close enough to various critical
        // values (typically 0.5, which yields a no-op for S and L shifts. 1/256 should
        // be small enough, but let's play it safe>
        const double epsilon = 0.0005;

        // Line processor: default/universal (i.e., old-school).
        void LineProcDefault(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            for(int x=0; x<width; ++x)
            {
                out[x] = SkPreMultiplyColor(gfx::HSLShift(
                    SkUnPreMultiply::PMColorToColor(in[x]), hsl_shift));
            }
        }

        // Line processor: no-op (i.e., copy).
        void LineProcCopy(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s<0 || fabs(hsl_shift.s-0.5)<HSLShift::epsilon);
            DCHECK(hsl_shift.l<0 || fabs(hsl_shift.l-0.5)<HSLShift::epsilon);
            memcpy(out, in, static_cast<size_t>(width)*sizeof(out[0]));
        }

        // Line processor: H no-op, S no-op, L decrease.
        void LineProcHnopSnopLdec(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            const uint32_t den = 65536;

            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s<0 || fabs(hsl_shift.s-0.5)<HSLShift::epsilon);
            DCHECK(hsl_shift.l<=0.5-HSLShift::epsilon && hsl_shift.l>=0);

            uint32_t ldec_num = static_cast<uint32_t>(hsl_shift.l * 2 * den);
            for(int x=0; x<width; ++x)
            {
                uint32_t a = SkGetPackedA32(in[x]);
                uint32_t r = SkGetPackedR32(in[x]);
                uint32_t g = SkGetPackedG32(in[x]);
                uint32_t b = SkGetPackedB32(in[x]);
                r = r * ldec_num / den;
                g = g * ldec_num / den;
                b = b * ldec_num / den;
                out[x] = SkPackARGB32(a, r, g, b);
            }
        }

        // Line processor: H no-op, S no-op, L increase.
        void LineProcHnopSnopLinc(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            const uint32_t den = 65536;

            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s<0 || fabs(hsl_shift.s-0.5)<HSLShift::epsilon);
            DCHECK(hsl_shift.l>=0.5+HSLShift::epsilon && hsl_shift.l<=1);

            uint32_t linc_num = static_cast<uint32_t>((hsl_shift.l - 0.5) * 2 * den);
            for(int x=0; x<width; ++x)
            {
                uint32_t a = SkGetPackedA32(in[x]);
                uint32_t r = SkGetPackedR32(in[x]);
                uint32_t g = SkGetPackedG32(in[x]);
                uint32_t b = SkGetPackedB32(in[x]);
                r += (a - r) * linc_num / den;
                g += (a - g) * linc_num / den;
                b += (a - b) * linc_num / den;
                out[x] = SkPackARGB32(a, r, g, b);
            }
        }

        // Saturation changes modifications in RGB
        //
        // (Note that as a further complication, the values we deal in are
        // premultiplied, so R/G/B values must be in the range 0..A. For mathematical
        // purposes, one may as well use r=R/A, g=G/A, b=B/A. Without loss of
        // generality, assume that R/G/B values are in the range 0..1.)
        //
        // Let Max = max(R,G,B), Min = min(R,G,B), and Med be the median value. Then L =
        // (Max+Min)/2. If L is to remain constant, Max+Min must also remain constant.
        //
        // For H to remain constant, first, the (numerical) order of R/G/B (from
        // smallest to largest) must remain the same. Second, all the ratios
        // (R-G)/(Max-Min), (R-B)/(Max-Min), (G-B)/(Max-Min) must remain constant (of
        // course, if Max = Min, then S = 0 and no saturation change is well-defined,
        // since H is not well-defined).
        //
        // Let C_max be a colour with value Max, C_min be one with value Min, and C_med
        // the remaining colour. Increasing saturation (to the maximum) is accomplished
        // by increasing the value of C_max while simultaneously decreasing C_min and
        // changing C_med so that the ratios are maintained; for the latter, it suffices
        // to keep (C_med-C_min)/(C_max-C_min) constant (and equal to
        // (Med-Min)/(Max-Min)).

        // Line processor: H no-op, S decrease, L no-op.
        void LineProcHnopSdecLnop(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s>=0 && hsl_shift.s<=0.5-HSLShift::epsilon);
            DCHECK(hsl_shift.l<0 || fabs(hsl_shift.l-0.5)<HSLShift::epsilon);

            const int32_t denom = 65536;
            int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
            for(int x=0; x<width; ++x)
            {
                int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
                int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
                int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
                int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

                int32_t vmax, vmin;
                if(r > g)
                {
                    // This uses 3 compares rather than 4.
                    vmax = std::max(r, b);
                    vmin = std::min(g, b);
                }
                else
                {
                    vmax = std::max(g, b);
                    vmin = std::min(r, b);
                }

                // Use denom * L to avoid rounding.
                int32_t denom_l = (vmax + vmin) * (denom / 2);
                int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

                r = (denom_l + r * s_numer - s_numer_l) / denom;
                g = (denom_l + g * s_numer - s_numer_l) / denom;
                b = (denom_l + b * s_numer - s_numer_l) / denom;
                out[x] = SkPackARGB32(a, r, g, b);
            }
        }

        // Line processor: H no-op, S decrease, L decrease.
        void LineProcHnopSdecLdec(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s>=0 && hsl_shift.s<=0.5-HSLShift::epsilon);
            DCHECK(hsl_shift.l>=0 && hsl_shift.l<=0.5-HSLShift::epsilon);

            // Can't be too big since we need room for denom*denom and a bit for sign.
            const int32_t denom = 1024;
            int32_t l_numer = static_cast<int32_t>(hsl_shift.l * 2 * denom);
            int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
            for(int x=0; x<width; ++x)
            {
                int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
                int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
                int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
                int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

                int32_t vmax, vmin;
                if(r > g)
                {
                    // This uses 3 compares rather than 4.
                    vmax = std::max(r, b);
                    vmin = std::min(g, b);
                }
                else
                {
                    vmax = std::max(g, b);
                    vmin = std::min(r, b);
                }

                // Use denom * L to avoid rounding.
                int32_t denom_l = (vmax + vmin) * (denom / 2);
                int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

                r = (denom_l + r * s_numer - s_numer_l) * l_numer / (denom * denom);
                g = (denom_l + g * s_numer - s_numer_l) * l_numer / (denom * denom);
                b = (denom_l + b * s_numer - s_numer_l) * l_numer / (denom * denom);
                out[x] = SkPackARGB32(a, r, g, b);
            }
        }

        // Line processor: H no-op, S decrease, L increase.
        void LineProcHnopSdecLinc(gfx::HSL hsl_shift, const SkPMColor* in,
            SkPMColor* out, int width)
        {
            DCHECK(hsl_shift.h < 0);
            DCHECK(hsl_shift.s>=0 && hsl_shift.s<=0.5-HSLShift::epsilon);
            DCHECK(hsl_shift.l>=0.5+HSLShift::epsilon && hsl_shift.l<=1);

            // Can't be too big since we need room for denom*denom and a bit for sign.
            const int32_t denom = 1024;
            int32_t l_numer = static_cast<int32_t>((hsl_shift.l - 0.5) * 2 * denom);
            int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
            for(int x=0; x<width; ++x)
            {
                int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
                int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
                int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
                int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

                int32_t vmax, vmin;
                if(r > g)
                {
                    // This uses 3 compares rather than 4.
                    vmax = std::max(r, b);
                    vmin = std::min(g, b);
                }
                else
                {
                    vmax = std::max(g, b);
                    vmin = std::min(r, b);
                }

                // Use denom * L to avoid rounding.
                int32_t denom_l = (vmax + vmin) * (denom / 2);
                int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

                r = denom_l + r * s_numer - s_numer_l;
                g = denom_l + g * s_numer - s_numer_l;
                b = denom_l + b * s_numer - s_numer_l;

                r = (r * denom + (a * denom - r) * l_numer) / (denom * denom);
                g = (g * denom + (a * denom - g) * l_numer) / (denom * denom);
                b = (b * denom + (a * denom - b) * l_numer) / (denom * denom);
                out[x] = SkPackARGB32(a, r, g, b);
            }
        }

        const LineProcessor kLineProcessors[kNumHOps][kNumSOps][kNumLOps] =
        {
            { // H: kOpHNone
                { // S: kOpSNone
                    LineProcCopy,         // L: kOpLNone
                    LineProcHnopSnopLdec, // L: kOpLDec
                    LineProcHnopSnopLinc  // L: kOpLInc
                },
                { // S: kOpSDec
                    LineProcHnopSdecLnop, // L: kOpLNone
                    LineProcHnopSdecLdec, // L: kOpLDec
                    LineProcHnopSdecLinc  // L: kOpLInc
                },
                { // S: kOpSInc
                    LineProcDefault, // L: kOpLNone
                    LineProcDefault, // L: kOpLDec
                    LineProcDefault  // L: kOpLInc
                }
            },
            { // H: kOpHShift
                { // S: kOpSNone
                    LineProcDefault, // L: kOpLNone
                    LineProcDefault, // L: kOpLDec
                    LineProcDefault  // L: kOpLInc
                },
                { // S: kOpSDec
                    LineProcDefault, // L: kOpLNone
                    LineProcDefault, // L: kOpLDec
                    LineProcDefault  // L: kOpLInc
                },
                { // S: kOpSInc
                    LineProcDefault, // L: kOpLNone
                    LineProcDefault, // L: kOpLDec
                    LineProcDefault  // L: kOpLInc
                }
            }
        };

    } //namespace HSLShift

}

// static
SkBitmap SkBitmapOperations::CreateHSLShiftedBitmap(
    const SkBitmap& bitmap, gfx::HSL hsl_shift)
{
    // Default to NOPs.
    HSLShift::OperationOnH H_op = HSLShift::kOpHNone;
    HSLShift::OperationOnS S_op = HSLShift::kOpSNone;
    HSLShift::OperationOnL L_op = HSLShift::kOpLNone;

    if(hsl_shift.h>=0 && hsl_shift.h<=1)
    {
        H_op = HSLShift::kOpHShift;
    }

    // Saturation shift: 0 -> fully desaturate, 0.5 -> NOP, 1 -> fully saturate.
    if(hsl_shift.s>=0 && hsl_shift.s<=(0.5-HSLShift::epsilon))
    {
        S_op = HSLShift::kOpSDec;
    }
    else if(hsl_shift.s >= (0.5+HSLShift::epsilon))
    {
        S_op = HSLShift::kOpSInc;
    }

    // Lightness shift: 0 -> black, 0.5 -> NOP, 1 -> white.
    if(hsl_shift.l>=0 && hsl_shift.l<=(0.5-HSLShift::epsilon))
    {
        L_op = HSLShift::kOpLDec;
    }
    else if(hsl_shift.l >= (0.5+HSLShift::epsilon))
    {
        L_op = HSLShift::kOpLInc;
    }

    HSLShift::LineProcessor line_proc =
        HSLShift::kLineProcessors[H_op][S_op][L_op];

    DCHECK(bitmap.empty() == false);
    DCHECK(bitmap.config() == SkBitmap::kARGB_8888_Config);

    SkBitmap shifted;
    shifted.setConfig(SkBitmap::kARGB_8888_Config,
        bitmap.width(), bitmap.height(), 0);
    shifted.allocPixels();
    shifted.eraseARGB(0, 0, 0, 0);
    shifted.setIsOpaque(false);

    SkAutoLockPixels lock_bitmap(bitmap);
    SkAutoLockPixels lock_shifted(shifted);

    // Loop through the pixels of the original bitmap.
    for(int y=0; y<bitmap.height(); ++y)
    {
        SkPMColor* pixels = bitmap.getAddr32(0, y);
        SkPMColor* tinted_pixels = shifted.getAddr32(0, y);

        (*line_proc)(hsl_shift, pixels, tinted_pixels, bitmap.width());
    }

    return shifted;
}

// static
SkBitmap SkBitmapOperations::CreateTiledBitmap(const SkBitmap& source,
                                               int src_x, int src_y,
                                               int dst_w, int dst_h)
{
    DCHECK(source.getConfig() == SkBitmap::kARGB_8888_Config);

    SkBitmap cropped;
    cropped.setConfig(SkBitmap::kARGB_8888_Config, dst_w, dst_h, 0);
    cropped.allocPixels();
    cropped.eraseARGB(0, 0, 0, 0);

    SkAutoLockPixels lock_source(source);
    SkAutoLockPixels lock_cropped(cropped);

    // Loop through the pixels of the original bitmap.
    for(int y=0; y<dst_h; ++y)
    {
        int y_pix = (src_y + y) % source.height();
        while(y_pix < 0)
        {
            y_pix += source.height();
        }

        uint32* source_row = source.getAddr32(0, y_pix);
        uint32* dst_row = cropped.getAddr32(0, y);

        for(int x=0; x<dst_w; ++x)
        {
            int x_pix = (src_x + x) % source.width();
            while(x_pix < 0)
            {
                x_pix += source.width();
            }

            dst_row[x] = source_row[x_pix];
        }
    }

    return cropped;
}

// static
SkBitmap SkBitmapOperations::DownsampleByTwoUntilSize(const SkBitmap& bitmap,
                                                      int min_w, int min_h)
{
    if((bitmap.width()<=min_w) || (bitmap.height()<=min_h) ||
        (min_w<0) || (min_h<0))
    {
        return bitmap;
    }

    // Since bitmaps are refcounted, this copy will be fast.
    SkBitmap current = bitmap;
    while((current.width()>=min_w*2) && (current.height()>=min_h*2) &&
        (current.width()>1) && (current.height()>1))
    {
        current = DownsampleByTwo(current);
    }
    return current;
}

// static
SkBitmap SkBitmapOperations::DownsampleByTwo(const SkBitmap& bitmap)
{
    // Handle the nop case.
    if((bitmap.width()<=1) || (bitmap.height()<=1))
    {
        return bitmap;
    }

    SkBitmap result;
    result.setConfig(SkBitmap::kARGB_8888_Config,
        (bitmap.width()+1)/2, (bitmap.height()+1)/2);
    result.allocPixels();

    SkAutoLockPixels lock(bitmap);

    const int resultLastX = result.width() - 1;
    const int srcLastX = bitmap.width() - 1;

    for(int dest_y=0; dest_y<result.height(); ++dest_y)
    {
        const int src_y = dest_y << 1;
        const SkPMColor* SK_RESTRICT cur_src0 = bitmap.getAddr32(0, src_y);
        const SkPMColor* SK_RESTRICT cur_src1 = cur_src0;
        if(src_y+1 < bitmap.height())
        {
            cur_src1 = bitmap.getAddr32(0, src_y + 1);
        }

        SkPMColor* SK_RESTRICT cur_dst = result.getAddr32(0, dest_y);

        for(int dest_x=0; dest_x<=resultLastX; ++dest_x)
        {
            // This code is based on downsampleby2_proc32 in SkBitmap.cpp. It is very
            // clever in that it does two channels at once: alpha and green ("ag")
            // and red and blue ("rb"). Each channel gets averaged across 4 pixels
            // to get the result.
            int bump_x = (dest_x << 1) < srcLastX;
            SkPMColor tmp, ag, rb;

            // Top left pixel of the 2x2 block.
            tmp = cur_src0[0];
            ag = (tmp >> 8) & 0xFF00FF;
            rb = tmp & 0xFF00FF;

            // Top right pixel of the 2x2 block.
            tmp = cur_src0[bump_x];
            ag += (tmp >> 8) & 0xFF00FF;
            rb += tmp & 0xFF00FF;

            // Bottom left pixel of the 2x2 block.
            tmp = cur_src1[0];
            ag += (tmp >> 8) & 0xFF00FF;
            rb += tmp & 0xFF00FF;

            // Bottom right pixel of the 2x2 block.
            tmp = cur_src1[bump_x];
            ag += (tmp >> 8) & 0xFF00FF;
            rb += tmp & 0xFF00FF;

            // Put the channels back together, dividing each by 4 to get the average.
            // |ag| has the alpha and green channels shifted right by 8 bits from
            // there they should end up, so shifting left by 6 gives them in the
            // correct position divided by 4.
            *cur_dst++ = ((rb >> 2) & 0xFF00FF) | ((ag << 6) & 0xFF00FF00);

            cur_src0 += 2;
            cur_src1 += 2;
        }
    }

    return result;
}

// static
SkBitmap SkBitmapOperations::UnPreMultiply(const SkBitmap& bitmap)
{
    if(bitmap.isNull())
    {
        return bitmap;
    }
    if(bitmap.isOpaque())
    {
        return bitmap;
    }

    SkBitmap opaque_bitmap;
    opaque_bitmap.setConfig(bitmap.config(), bitmap.width(), bitmap.height());
    opaque_bitmap.allocPixels();

    {
        SkAutoLockPixels bitmap_lock(bitmap);
        SkAutoLockPixels opaque_bitmap_lock(opaque_bitmap);
        for(int y=0; y<opaque_bitmap.height(); ++y)
        {
            for(int x=0; x<opaque_bitmap.width(); ++x)
            {
                uint32 src_pixel = *bitmap.getAddr32(x, y);
                uint32* dst_pixel = opaque_bitmap.getAddr32(x, y);
                SkColor unmultiplied = SkUnPreMultiply::PMColorToColor(src_pixel);
                *dst_pixel = unmultiplied;
            }
        }
    }

    opaque_bitmap.setIsOpaque(true);
    return opaque_bitmap;
}

// static
SkBitmap SkBitmapOperations::CreateTransposedBtmap(const SkBitmap& image)
{
    DCHECK(image.config() == SkBitmap::kARGB_8888_Config);

    SkAutoLockPixels lock_image(image);

    SkBitmap transposed;
    transposed.setConfig(SkBitmap::kARGB_8888_Config,
        image.height(), image.width(), 0);
    transposed.allocPixels();
    transposed.eraseARGB(0, 0, 0, 0);

    for(int y=0; y<image.height(); ++y)
    {
        uint32* image_row = image.getAddr32(0, y);
        for(int x=0; x<image.width(); ++x)
        {
            uint32* dst = transposed.getAddr32(y, x);
            *dst = image_row[x];
        }
    }

    return transposed;
}